1. Field of the Invention
The present invention relates to a balance with a weighing cell including a measurement transducer with a short travel distance and a device for protecting the load cell against dynamic and static overload. The protecting device includes a spring mounted in the flux of force between the load application and the load cell and a travel-limiting stop member fixedly attached to a housing.
2. Description of the Related Art
Each balance is designed for a predetermined load range which may not be exceeded or only slightly exceeded. In order to protect balances against damage, they are usually equipped with an overload protecting device which includes a stop member which prevents, for example, a plastic deformation or which generally prevents that a predetermined travel path of the load receiving means is exceeded. Such overload protections which consist of a stop member become fully effective when the maximum load is slowly or statically exceeded and the balance mechanism is protected by limiting travel by means of the stop member. However, in cases of dynamic overloads, for example, when a load is dropped onto the weighing dish, a stop member is no longer sufficient because the acceleration forces subject the balance mechanism during the initial 20 to 40 ms to tension forces as well as to compression forces which may lead to damage of the balance.
German Utility Model 79 35 202 discloses an overload protection for a balance with electromagnetic load compensation in which the load receiving means is supported on the suspension unit with a compression spring being mounted between the load receiving means and the suspension unit. When a high dynamic load is applied to the weighing dish, the load receiving means can slide downwardly on a stop member while overcoming the spring force in the suspension unit, and, thus, the suspension unit with the balance mechanism is protected against the impact which has been produced, i.e., the suspension unit with the balance mechanism is protected against the primary effect of the dynamic overload. When the spring untensions, which occurs within milliseconds, the load receiving means is thrown in the opposite direction as a result of the secondary effect of the dynamic overload and the impact of the load receiving means against the suspension unit may result in upsetting-type damage of coupling members or other components of the balance mechanism.
It is, therefore, the primary object of the present invention to provide an overload protection for balances having a load cell including an instrument transformer with a short travel distance, in which the balance mechanism is protected against the primary effect as well as against the secondary effect of a dynamic overload.